Phosphorescence spectra of the copper complexes of proto-, copro-and uroporphyrins have been obtained. The phosphorescence intensities are linear in the region of 10 to the minus 8 to 10 to the minus 4 M. By varying the wavelength of excitation, differences in the emission band intensities characterize the various porphyrins so that a determination of each in a mixture can be accomplished. The two applications for which this difference method is most germane are the ratio of proto- and uroporphyrins in blood and the ratio of copro-and uroporphyrins in urine and feces. A very stable synthetic standard which is commercially available (copper tetraphenylporphyrin) has been evaluated. This porphyrin species phosphoresces at 725nm upon excitation at 420nm while the copper complexes of natural porphyrins (proto-, copro- and uroporphyrins) phosphoresce in the region of 680nm upon excitation in the region of 405 nm. The spectral differences allow facile determination of porphyrin concentration. Somewhat apart from the use of phosphorescence spectroscopy for porphyrin detemination have been our efforts to improve fluorescence determinations. The use of fluorescence methods is widespread and offers substantial improvement in sensitivity over absorption spectroscopy. There are problems with interferences, however, which we would like to overcome. It would be advantageous to develop more stable standards than those currently in use, as well. To overcome the problem of interference, we have developed a difference method involving taking the fluorescence spectrum, complexation of ZN (II) to the porphyrins, and recording of a second spectrum. At 650nm the ZN (II) porphyrins complexes have essentially no fluorescence intensity while the free porphyrins exhibit large intensites. The intensity difference upon complexation gives a more accurate determination than the intensity recorded for the unmodified sample. This technique- coupled with the ion exchange column separation- has been applied to the determination of copro- and uropophyrins in urine. The procedure takes about fifteen minutes. The stable standard evaluated for this procedure is the synthetic porphyrin- zinc tetraphenylporphyrin.